In single spool turboshaft gas turbine engines in propeller-type aircraft propulsion applications, the compressor, the turbine and the output shaft all rotate as a unit. If such engines are shutdown in flight, the pitch of the propeller blades can be adjusted to extract energy from the airstream around the aircraft to backdrive the compressor to provide enough compressed air to sustain an in-flight restart. In free power turbine type engines and other multiple spool gas turbine engines, the propellers are driven by a turbine which rotates independently of the gas generator of the engine so that the propeller blades are ineffective to backdrive the gas generator compressor. Accordingly, aircraft equipped with such engines must also be equipped with in-flight starting assist devices such as auxiliary power units (APU's). An in-flight starting mechanism according to this invention selectively and automatically positively connects the propeller driving turbine rotor to the gas generator rotor so that in-flight restarts can be effected without APU's or like auxiliary devices.